The disclosure relates to a method for manufacturing a spherical-cap-shaped recess in a drive shaft, to a drive shaft comprising said recess, and to a hydrostatic axial piston machine comprising the drive shaft.
A hydrostatic axial piston machine has a drive shaft with a drive flange provided on the end face with a plurality of spherical-cap-shaped recesses arranged on a pitch circle. Ball heads of working pistons and a guide piston of a cylinder drum of the axial piston machine are received pivotably in said recesses. In this case, the working pistons plunge into cylinder bores of the cylinder drum and are received therein so as to be axially displaceable, in order to transmit torque to the drive shaft in motor operation, and alternatively in pump operation to convey pressure medium to the high-pressure side, in the event of a change in pressure and on account of the inclined position of the drive shaft in relation to the cylinder drum.
To ensure that the axial piston machine is operated as intended, the spherical-cap-shaped recesses, just like the ball heads, have to satisfy specifications with respect to their dimensional tolerance, in particular the circularity, and their wear behavior.
For manufacturing, methods are known in which the recesses are shaped by cutting by means of whirling and subsequently provided with a hard wear layer by means of a heat treatment, in particular by means of gas nitrocarburizing (GNC). Corresponding gas nitrocarburizing is proposed for cylinder bores of a cylinder drum in the document DE 10 2013 226 090 A1.
The methods known to date have the disadvantage that the wear layer which is formed during the GNC is relatively brittle, non-uniform and thick, and therefore it has to be reworked. In order to satisfy the tolerances and to avoid sections of the wear layer breaking away during operation, the latter therefore customarily has to be ground in a third method step and then finished. In this way, firstly the thickness of the wear layer is reduced in such a manner that the required tolerance in relation to the circularity of the recess is observed, and secondly the susceptibility to brittle fracture is reduced. Finishing for spherical outer surfaces is disclosed, for example, in the laid-open specification DE 2 102 461. A disadvantage of this is the fact that the finishing step is costly and time-consuming.
In this respect, the disclosure is based on the object of providing a less costly and/or time-consuming method for manufacturing the spherical-cap-shaped recess. Furthermore, the disclosure is based on the object of providing a drive shaft comprising such a recess and a hydrostatic axial piston machine comprising such a drive shaft.